1. Field of the Invention
The present invention relates to a zoom lens system suitable for a single-lens reflex camera and a digital camera, an imaging apparatus, and a method for varying a focal length of the zoom lens system.
2. Related Background Art
There has been proposed a four-lens-group zoom lens systems composed of, in order from an object, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, and a fourth lens group having positive refractive power in Japanese Patent Application Laid-Open No. 2000-338397.
Although the conventional zoom lens system has a wide angle of view and a given zoom ratio as a standard zoom lens system and is compact and lightweight with a reasonable price, it has been difficult to obtain preferable optical performance over entire zoom range. Accordingly, higher optical performance has been expected in such a zoom lens system.